1. Field of the Invention
The present invention relates to technical fields of surface light source devices and image display apparatuses. In particular, the present invention relates to a technical field for reducing the thickness of such a device and an apparatus and for suppressing nonuniformity in brightness thereof by providing projections having predetermined shapes, to a light-controlling member that controls light emitted from a light source.
2. Description of the Related Art
There are surface light source devices in which light sources such as cold-cathode fluorescent lamps (CCFLs) or light-emitting diodes (LEDs) are used for illumination. Such a surface light source device is used as an illumination device in which the light source serves as a direct illumination, or is included in an image display apparatus, such as a television receiver or a personal computer, in which the light source serves as a backlight illumination.
Examples of the image display apparatus include a liquid crystal display apparatus in which a liquid crystal panel serves as a display panel that displays an image.
Since the liquid crystal panel of the liquid crystal display apparatus is not a self-luminous display, the liquid crystal display apparatus includes a surface light source device having a light source that illuminates the liquid crystal panel from the rear side. In this case, the surface light source device is used as a backlight device that illuminates the liquid crystal panel from the rear side.
Surface light source devices used as backlight devices are classified into the following: a so-called side-edge device in which a light source is disposed on a lateral side of a light-guiding member that guides light emitted from the light source in a predetermined direction, whereby a display panel is illuminated; and a so-called direct-lighting device in which a light source is disposed on the rear side of a display panel and light emitted from the light source is directed toward the display panel.
Liquid crystal display apparatuses used as television receivers and liquid crystal display apparatuses of large sizes typically include direct-lighting backlight devices as surface light source devices, out of the importance of obtaining bright images.
In general, a surface light source device included in a liquid crystal display apparatus includes a diffusing member (a diffusing plate or sheet) facing the rear surface of a liquid crystal panel, and a reflecting member disposed on the rear side of the diffusing member.
For example, in the surface light source device, a plurality of fluorescent lamps, such as CCFLs, serving as light sources are arranged in a predetermined direction, and the diffusing member is disposed between the display panel and the fluorescent lamps. The diffusing member causes light emitted from the fluorescent lamps to be applied uniformly to the display panel by diffusing the light, thereby preventing the contours of the fluorescent lamps from being visible through the display panel to a user, that is, preventing the existence of the fluorescent lamps from being recognized as a lamp image.
The diffusing member, causing the light emitted from the light source to be uniformly applied to the liquid crystal panel, provides uniformity in brightness on a display screen of the liquid crystal panel.
In the liquid crystal display apparatus, when light is emitted from the light source, the emitted light is diffused by the diffusing member and is output therefrom to the rear surface of the liquid crystal panel on which an image is being displayed. The light of the light source is emitted not only toward the diffusing member but also toward the reflecting member. The light emitted toward the reflecting member is reflected by the reflecting member, enters the diffusing member, is diffused by the diffusing member, and is applied to the liquid crystal panel.
In recent years, there has been an increasing demand that liquid crystal display apparatuses such as the one described above be thinner. If it is attempted to reduce the thickness of such an apparatus by reducing the interval between the light source and the diffusing member, a problem arises in that the existence of lamps may be recognized as a lamp image, as described above.
To avoid this, there is a surface light source device in which a light-controlling member called a prism array is disposed between a light source and a diffusing member. In this device, light emitted straight ahead from the light source is reflected by the light-controlling member in such a manner that the brightness at a region directly in front of the light source is reduced, whereby the occurrence of a visible lamp image is suppressed while the thickness of the device is reduced.
In the surface light source device described above, although prevention of the occurrence of a visible lamp image and reduction of the device thickness can be realized simultaneously, the brightness at a region directly in front of the light source is reduced too much, whereas the brightness near the region directly in front of the light source increases. This leads to a problem in that nonuniformity in brightness increases.
To avoid this, referring to FIG. 9, a surface light source device disclosed in Japanese Unexamined Patent Application Publication No. 2006-162827 includes a prism array (light-controlling member) a having prisms b of oval semi-cylinder shape. In this device, some of light A incident on the prism array a in a direction of a normal L (the thickness direction of the prism array a) is transmitted therethrough, whereas most of light B incident on the prism array a at an oblique angle with respect to the normal L is transmitted therethrough. Thus, the amount of luminous flux of light that is output from the prism array a is made uniform. Consequently, nonuniformity in brightness is suppressed.